A mobile ad-hoc network includes a number of geographically distributed, potentially mobile nodes wirelessly connected by one or more radio frequency channels. Compared with other type of networks, such as cellular networks or satellite networks, the most distinctive feature of mobile ad hoc networks is the lack of fixed infrastructure. The network is formed of mobile nodes, and a network is created on the fly as the nodes transmit to or receive from other nodes. The network does not in general depend on a particular node and dynamically adjusts as some nodes join or others leave the network.
In an environment where a fixed communication infrastructure is unreliable or unavailable, such as in a natural disaster area struck by earthquake or hurricane, an ad hoc network can be quickly deployed and provide much needed communications. Ad hoc networks may allow people to exchange data in the field or in a classroom without using any network structure except the one they create by simply turning on their computers or PDAs.
As wireless communication increasingly permeates everyday life, new applications for mobile ad hoc networks will continue to emerge and become an important part of the communication structure. Mobile ad hoc networks may pose serious challenges to the designers. Due to the lack of a fixed infrastructure, nodes self-organize and reconfigure as they move, join or leave the network. All nodes could potentially be functionally identical and there may not be any natural hierarchy or central controller in the network. Many network-controlling functions are typically distributed among the nodes. Nodes are often powered by batteries and have limited communication and computation capabilities. The bandwidth of the system is usually limited. The distance between two nodes often exceeds the radio transmission range, and a transmission has to be relayed by other nodes before reaching its destination. Consequently, a MANET typically has a multi-hop topology, and this topology changes as the nodes move around.
The Mobile Ad-Hoc Networks (MANET) working group of the Internet Engineering Task Force (IETF) has been actively evaluating and standardizing routing, including multicasting, protocols. Because the network topology changes arbitrarily as the nodes move, information is subject to becoming obsolete, and different nodes often have different views of the network, both in time (information may be outdated at some nodes but current at others) and in space (a node may only know the network topology in its neighborhood usually not far away from itself).
A routing protocol desirably adapts to frequent topology changes and with less accurate information. Because of these unique requirements, routing in these networks is very different from others. Gathering fresh information about the entire network is often costly and impractical. Many routing protocols are reactive (on-demand) protocols: they collect routing information only when necessary and to destinations they need routes to, and do not generally maintain unused routes after some period of time. Accordingly, the routing overhead is greatly reduced compared to pro-active protocols which maintain routes to all destinations at all times. It may be important for a protocol to be adaptive. Ad Hoc on Demand Distance Vector (AODV), Dynamic Source Routing (DSR) and Temporally Ordered Routing Algorithm (TORA) are representative of on-demand routing protocols presented at the MANET working group.
Examples of other various routing protocols include Destination-Sequenced Distance Vector (DSDV) routing which is disclosed in U.S. Pat. No. 5,412,654 to Perkins, and Zone Routing Protocol (ZRP) which is disclosed in U.S. Pat. No. 6,304,556 to Haas. ZRP is a hybrid protocol using both proactive and reactive approaches based upon distance from a source node. The Temporal Transition Network Protocol (TTNP), discussed in U.S. Pat. No. 6,754,192 assigned to the present assignee Harris Corp. of Melbourne, Fla., is another hybrid protocol that includes building and updating route tables at each node by managing and controlling the application of either proactive or reactive route discovery and their respective associated processes to define and maintain routes in the network based upon predicted route stability.
These conventional routing protocols typically use a best effort approach in selecting a route from the source node to the destination node. Typically, the number of hops is the main criteria (metric) in such a best effort approach. In other words, the route with the least amount of hops is selected as the transmission route.
Unlike fixed immobile networks, in a MANET a given node is presented with a changing set of neighbors from which a subset is selected and to which connections or links will be made. Current state of the art neighbor connection management algorithms typically use only local (two or three hop) link layer information. Commercial and government customers may need robust topologies and enhanced QoS in a dynamic mobile mesh. Accordingly, there is a need to enhance QoS, latency and resistance to link and node failures in such dynamic mobile networks.